Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications such as angina pectoralis and incontinence. Deep Brain Stimulation (DBS) has also been applied therapeutically for well over a decade for the treatment of refractory chronic pain syndromes, and DBS has also recently been applied in additional areas such as movement disorders and epilepsy. Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation. Functional Electrical Stimulation (FES) systems such as the Freehand system by NeuroControl (Cleveland, Ohio) have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
Each of these implantable neurostimulation systems typically includes one or more therapy delivery elements implanted at the desired stimulation site and an implantable neurostimulator, such as an implantable pulse generator (IPG), implanted remotely from the stimulation site, but coupled either directly to the therapy delivery elements or indirectly to the therapy delivery elements via one or more extensions in cases where the length of the therapy delivery elements is insufficient to reach the IPG. In some cases, the extension leads may be used to facilitate coupling of the neurostimulator, which may otherwise be incompatible with the therapy delivery elements or extension leads, thereto. Thus, electrical pulses can be delivered from the neurostimulator to the therapy delivery elements to stimulate the tissue and provide the desired efficacious therapy to the patient.
In the context of an SCS procedure, one or more therapy delivery elements are introduced through the patient's back into the epidural space under fluoroscopy, such that the electrodes carried by the leads are arranged in a desired pattern and spacing to create an electrode array. The specific procedure used to implant the therapy delivery elements will ultimately depend on the type of therapy delivery elements used. Currently, there are two types of commercially available therapy delivery elements: a percutaneous lead and a surgical lead.
A percutaneous lead includes a cylindrical body with ring electrodes, and can be introduced into contact with the affected spinal tissue through a Touhy-like needle, which passes through the skin, between the desired vertebrae, and into the epidural space above the dura layer. For unilateral pain, a percutaneous lead is placed on the corresponding lateral side of the spinal cord. For bilateral pain, a percutaneous lead is placed down the midline of the spinal cord, or two percutaneous leads are placed down the respective sides of the midline. In many cases, a stylet, such as a metallic wire, is inserted into a lumen running through the center of each of the percutaneous leads to aid in insertion of the lead through the needle and into the epidural space. The stylet gives the lead rigidity during positioning, and once the lead is positioned, the stylet can be removed after which the lead becomes flaccid.
As a patient implanted with a therapy delivery element moves, some regions of the body may expand and contract, resulting in changes in length. The movement may exert high loading forces on anchors, therapy delivery elements, lead extensions, or body tissue. These forces may cause lead failure, axial migration of electrodes, anchor damage, or tissue damage. The patient may experience pain or operational failure or performance degradation of the therapy delivery elements.
U.S. Pat. No. 7,831,311 (Cross, et al.) is directed to implantable leads with a lead body construction designed to accommodate loading forces exerted on the lead body during patient movement. The lead body is sufficiently stretchable to resist forces that could otherwise cause lead failure, axial migration of the electrodes, anchor damage, or tissue damage. The lead body may include a variety of features that reduce the axial stiffness of the lead without significantly impacting the operation and structural integrity of lead components, such as electrodes, conductors and insulators. For example, a lead body may include a low durometer outer jacket and/or conductors with a low modulus of elasticity, providing increased stretchability. Increasing stretchability of a lead body can also increase the vulnerability of the lead body to flex fatigue, buckling fatigue, kinking, and crush. In some embodiments, the lead may also include a coiled wire stylet guide to provide enhanced column strength. The coiled wire stylet guide may or may not be electrically conductive.